源码理解 UE4中的 FCookStatsManager::FAutoRegisterCallback RegisterCookStats

官方文档：https://dev.epicgames.com/documentation/zh-cn/unreal-engine/API/Runtime/Core/ProfilingDebugging/FCookStatsManager文档中的注释：
When a cook a complete that is configured to use stats (ENABLE_COOK_STATS), it will broadcast this delegate, which, when called, gives you a TFunction to call to report each of your stats.代码：
FCookStatsManager::FAutoRegisterCallback RegisterCookStats([](FCookStatsManager::AddStatFuncRef AddStat)
{ ……

首先，RegisterCookStats是一个全局（非静态）变量，它的类型是 FCookStatsManager::FAutoRegisterCallback ，它调用的初始化器是 ( []()...  ) ，也就是说，传入了一个lambda函数，作为初始化器的参数。

那么看FCookStatsManager::FAutoRegisterCallback的声明如下，可以得知，所有声明一个 FCookStatsManager::FAutoRegisterCallback 结构体，本质上就是给 static CookStatsCallbacks 静态变量添加元素（也就是该lambda方法）。

/** Use this to register a callback to gather cook stats for a translation unit. When a cook is finished, this delegate will be fired. */
static CORE_API FGatherCookStatsDelegate CookStatsCallbacks;/** Called after the cook is finished to gather the stats. */
static CORE_API void LogCookStats(AddStatFuncRef AddStat);/** Helper struct to auto-register your STATIC FUNCTION with CookStatsCallbacks */
struct FAutoRegisterCallback
{template<typename Func>explicit FAutoRegisterCallback(Func Callback){CookStatsCallbacks.AddLambda(Callback);}
};